Fuel cells have been proposed as a power source for electric vehicles and other applications. One such fuel cell is the PEM (i.e. Proton Exchange Membrane) fuel cell that includes a so-called “membrane-electrode-assembly” (MEA) comprising a thin, solid polymer membrane-electrolyte having a pair of electrodes (i.e., an anode and a cathode) on opposite faces of the membrane-electrolyte. The MEA is sandwiched between a pair of electrically conductive fluid distribution elements (i.e., bipolar plates) which serve as current collectors for the electrodes, and contain a so-called “flow field” which is an array of lands and grooves formed in the surface of the plate contacting the MEA. The lands conduct current from the electrodes, while the grooves between the lands serve to distribute the fuel cell's gaseous reactants evenly over the faces of the electrodes. Gas diffusion media, which are typically porous graphite/carbon paper, are positioned between each of the electrically conductive fluid distribution elements and the electrode faces of the MEA, to support the MEA where it confronts grooves in the flow field, and to conduct current therefrom to the adjacent lands.
The gas diffusion media heretofore interposed between the electrodes and their associated electrode plates have drawbacks, however. Gas diffusion media usually comprise a mat of randomly oriented fibers that are typically about 10 mils thick, and are quite expensive. Gas diffusion media also impede diffusion of the H2 and O2 to their respective electrodes, require that considerable pressure be applied to ends of the cell/stack to provide a good conductive interface with the electrodes and thereby reduce cell impedance, and impede the outflow of water from the MEA.
Of the above drawbacks, the phenomenon of impeding the outflow of water from the MEA, often referred to as “flooding” is particularly troublesome. Flooding can hinder a fuel cell's operation at low current density when the air flow through the cathode flow field plate is not sufficient to drive the water removal process. Excess liquid water also tends to plug the pores in gas diffusion media, and thereby isolate the catalytic sites from the reactant oxygen flow. Therefore, there is a need for an improved fuel cell design to minimize the aforesaid drawbacks.